1. Field of the Invention
The present invention relates to a method for producing a liquid crystal display device having a flat display, such as a portable information terminal, a personal computer, a word processor, an amusement apparatus, and a television set usable by a large number of people, and a liquid crystal display device used for a display board utilizing a shutter effect, a window, a door, a wall, and the like.
1. Description of the Related Art
Japanese Laid-Open Publication No. 6-301015 (U.S. Pat. No. 5,473,450) discloses a liquid crystal display device 100 (FIG. 13) having viewing angle characteristics remarkably improved by orienting liquid crystal molecules axis-symmetrically (e.g., radially, concentrically, or the like).
A partial cross section of the conventional liquid crystal display device 100 is shown schematically in FIG. 13. In the liquid crystal display device 100, a liquid crystal layer 27 held between a pair of substrates 21 and 23 includes a polymeric region 28 and a liquid crystal region 29 substantially surrounded by the polymeric region 28. The liquid crystal region 29 is formed so as to correspond to a pixel defined by an area between each electrode 22 and a portion of electrode 24 opposed to each electrode 22. Liquid crystal molecules (not shown) in the liquid crystal region 29 are oriented axis-symmetrically with respect to a center axis of the liquid crystal region 29 which is perpendicular to the substrates 21 and 23. As a result, the liquid crystal display device 100 has wide viewing angle characteristics.
A conventional method for producing the liquid crystal display device 100 requires a five-step process of manipulating temperature and voltage shown in FIGS. 7A and 7B in order to axis-symmetrically orient the liquid crystal molecules in a pixel region 25 surrounded by the polymeric region 28. The five steps will be described below.
(1) A step of maintaining a precursor mixture containing a liquid crystal material and a polymerizable material at a temperature at which the precursor mixture enters an isotropic phase (time 0-t1 in FIG. 7A). The temperature is equivalent to or higher than the miscible temperature of the precursor mixture. A pixel of the liquid crystal display device 100 is observed with a polarizing microscope from a direction perpendicular to a display surface (i.e. substrate 21 and 23; a crossed-Nicols state). The state of the pixel in this step is shown in FIG. 8A. The entire pixel is in an isotropic phase 10. The isotropic phase 10 is observed as a dark viewfield, but shown as a white viewfield in FIGS. 8A, 8B, 8C, 8D and BE for the sake of clarity.
(2) A step of gradually cooling and maintaining the precursor mixture which, in the entirety thereof, is the isotropic phase 10 and is in a miscible state in order to separate a liquid crystal droplet 11a (i.e., liquid crystal phase 11) from the isotropic phase 10 (time t1-t3 in FIG. 7A). The state of the pixel in this step is shown in FIG. 8B. The liquid crystal droplet 11a separates from the isotropic phase 10, and as a result, two phases (that is, the isotropic phase 10 and the liquid crystal phase 11) are generated in the pixel.
(3) A step of raising the temperature of the resultant precursor mixture in which the isotropic phase 10 and the liquid crystal phase 11 exist in order to reduce the size of the liquid crystal droplet 11a to facilitate the axis-symmetrical orientation of the liquid crystal molecules therein (time t3-t4 in FIG. 7A). The state of the pixel in this step is shown in FIG. 8C. Two phases (that is, the isotropic phase 10 and the liquid crystal phase 11) exist in the pixel, and the liquid crystal phase 11 is of a size which would allow the liquid crystal molecules therein to be oriented axis-symmetrically with an application of voltage.
(4) A step of applying a voltage to the precursor mixture while maintaining the size of the liquid crystal droplet 11a obtained in step (3) above in order to cause the liquid crystal molecules in the liquid crystal droplet 11a to be axis-symmetrically oriented (time t4-t5 in FIG. 7A). The state of the pixel in this step is shown in FIG. 8D. Two phases (that is, the isotropic phase 10 and the liquid crystal phase 11) exist in the pixel. The liquid crystal molecules in the liquid crystal droplet 11a are axis-symmetrically oriented, and as a result, an extinction pattern 12 consisting of four (4) portions is observed.
(5) A step of gradually cooling the precursor mixture in order to cause the liquid crystal droplet 11a having the axis-symmetrical orientation to grow (time t5-t6 in FIG. 7A). The state of the pixel in this step is shown in FIG. 8E. The liquid crystal droplet 11a having the axis-symmetrical orientation extends over the entirety of the pixel.
As is described above, in the conventional technology, it is necessary to precisely control the temperature and the timing of a voltage application for axis-symmetrically orienting the liquid crystal molecules in the liquid crystal droplet 11a. The temperature of the precursor mixture must be controlled and maintained so that the temperature allows the liquid crystal droplet 11a to be of a size which facilitates the axis-symmetrical orientation of the liquid crystal molecules therein. A voltage must be applied to the precursor mixture while maintaining this temperature.